This invention relates to a seal within a micro electro-mechanical (MEM) device. The invention has application in ejection nozzles of the type that are fabricated by integrating the technologies applicable to micro electro-mechanical systems (MEMS) and complimentary metal-oxide semiconductor (xe2x80x9cCMOSxe2x80x9d) integrated circuits, and the invention is hereinafter described in the context of that application. However, it will be understood that the invention does have broader application to seals within various types of MEM devices.
A high speed page width ink jet printer has recently been developed by the present applicant. This typically employs in the order of 51, 200 ink jet nozzles to print on A4 size paper to provide photographic quality image printing at 1,600 dpi. In order to achieve this nozzle density, the nozzles are fabricated by integrating MEMS-CMOS technology and in this context reference may be made to International Patent Application No. PCT/AU00/00338 lodged by the present applicant and entitled xe2x80x9cThermal Actuatorxe2x80x9d.
These high speed page width ink jet printers produce an image on a sheet by causing an actuator arm to move relative to a substrate by forming the actuating arm in part from an electrically resistive material and by applying a current to the arm to effect movement of the arm. The arm is connected to a paddle so that upon movement of the arm the paddle is moved to eject a droplet of ink onto the sheet. In order to eject the droplet of ink the paddle extends into a nozzle chamber which has a nozzle aperture and movement of the paddle causes the droplet to be ejected from the nozzle aperture. It is therefore necessary for the actuator arm and the paddle to move relative to the nozzle chamber in order to effect ejection of the droplet. Also, in view of the need for the actuator arm and paddle to move relative to the nozzle chamber there is also a need to seal the nozzle chamber where the actuator arm enters the chamber so the ink does not spuriously leak from the chamber during operation of the printer.
The present invention provides a micro electromechanical device comprising;
a fluid chamber for containing a fluid, the fluid chamber having a first chamber wall, the chamber wall having a substantially straight peripheral edge portion;
an outlet aperture in the chamber wall for allowing exit of fluid from the chamber;
an actuator aperture defined partly by said edge portion of the chamber wall;
an actuator extending into said chamber through the actuator aperture and being moveable to dispense fluid from the chamber through the outlet aperture;
a second wall carried by the actuator and covering at least a part of said actuator aperture, the second wall being substantially planar and moveable relative to the edge portion of the chamber wall when the actuator moves to dispense fluid from the chamber; and
when the actuator moves in the chamber to dispense fluid from the chamber the second wall moves in closely spaced apart relationship with respect to the edge portion so that a meniscus is formed between the edge portion and second wall by fluid within the chamber thereby creating a seal between the edge portion and the second wall.
Preferably the second wall substantially entirely covers the actuator aperture.
Preferably the second wall is provided on a block coupled to the actuator.
Preferably the block is substantially rectangular in configuration.
Preferably the second wall has a width in a direction perpendicular to the direction of movement of the actuator which is substantially the same as the length of the straight edge portion of the chamber wall.
Preferably the actuator includes an upper arm portion and an lower arm portion, the upper arm portion having an opening and a portion of the block including a flange projecting through said opening to facilitate coupling of the block to the actuator.
Preferably the second wall is spaced from the edge portion of the chamber wall by a distance of less than one micron when the actuator is in a rest position.
Preferably the actuator is coupled to a paddle arranged within the chamber for the ejection of fluid in the form of droplets from the chamber upon movement of the actuator.
Preferably the actuator is supported at one end in a support structure and electrical circuit elements for operation of the device are embodied in CMOS structures within or on the support structure.
Preferably the chamber wall and the block having the second wall are formed by deposition at the same time and wherein the block has an upper surface which is substantially level with the chamber wall when the actuator is in the rest position.
Preferably a lip is formed on the edge portion which extends outwardly of the chamber the second wall also has a lip which extends outwardly of the chamber.